Mechanical and optical properties of polyurethane‐polystyrene two‐phase polymers

The mechanical and optical properties have been examined of a series of polyurethane‐polystyrene two‐phase systems produced by simultaneous polymerization. Torsion pendulum data show two separate glass transitions which are essentially those of the constituent homopolymers. Thus these systems do not from true interpenetrating networks. Phase inversion from a continuous polyurethane to a continuous polystyrene phase occurred at the relatively low styrene concentration of 20 to 25%. Measurements of the stress‐optical coefficients supported this finding. When polystyrene formed the continuous phase, straining produced softening at strains below about 15 percent. Birefringence measurements indicated that the rubbery polyurethane domains did not orient in these compositions. The stress‐optical coefficients showed no time dependence. The strain‐optical coefficients decreased with increasing temperature.